1. Field of the Invention
This invention relates to a camera and to a method of controlling the operation thereof.
2. Description of the Related Art
There is a digital camera equipped with a device having both optical and electronic finders (Patent Document 1). The fine optical image of a subject can be seen by using the optical finder, and the image of a subject identical with the captured image of the subject can be seen by using the electronic finder.
Further, there is a camera in which a partial image clipped from a subordinate image obtained from the image sensor of a subordinate imaging unit is superimposed upon a main image obtained from the image sensor of a main imaging unit (Patent Document 2), as well as a camera in which the operation of a conventional image coincidence optical rangefinder is performed by superimposing images from two image sensing devices (Patent Document 3). Furthermore, there is a camera in which pixels to be used in a parallax calculation are selected suitably upon taking into consideration processing time relating to the parallax calculation (Patent Document 4), and a camera in which it is possible to set shooting conditions in accordance with a cropping area (Patent Document 4).
Patent Document 1: Japanese Patent Application Laid-Open No. 2012-65294
Patent Document 2: Japanese Patent Application Laid-Open No. 2011-135490
Patent Document 3: Japanese Patent Application Laid-Open No. 2007-163724
Patent Document 4: Japanese Patent Application Laid-Open No. 2012-18013
Patent Document 5: Japanese Patent Application Laid-Open No. 2007-201779
Cameras heretofore referred to as high-performance cameras are equipped with a double-image coincidence rangefinder which, when the user performs focusing while looking at the finder device, is such that the image of the subject becomes a pair of offset images if the image of the subject is out of focus, although such offset vanishes when the image of the subject is brought into focus. Hence there is a need to arrange it so that the double-image coincidence system can be applied also to a camera having both the optical and electronic finders mentioned above. However, none of Patent Documents 1 to 5 give any consideration whatsoever to the application of the double-image coincidence system to such an optical/electronic viewfinder. In a case where the double-image coincidence system is applied, a conceivable arrangement is to superimpose the image of a subject that is the result of optical formation and an image that lies within an AF target area displayed on a display screen, where the image in the AF target area is from within the image of the subject obtained by imaging using a solid-state electronic image sensing device. In a case where the double-image coincidence system is applied to a camera having both the optical and electronic finders mentioned above, the time needed to display an image on the display unit is delayed by the length of time needed for a readout from the solid-state electronic image sensing device. If the subject or the camera is moving, the optical image of the subject and the AF target image being displayed on the display unit will not coincide. As a result, not only does the user experience a sense of discomfort but the user may also judge that the subject is out of focus even though the subject is in focus.